Manchester City coach Pep Guardiola saw his side move back to third place in the Premier League but warned that leaders Chelsea "are almost unstoppable."
Goals from Sergio Aguero and Leroy Sane left City eight points behind Antonio Conte's team, who face West Ham on Monday.
Guardiola told his postmatch news conference: "It's three more points. We are there behind, of course, Chelsea because they are almost unstoppable.
"It's a pity that the distance between us and Chelsea is so big.
"We started the season winning 10 games in a row, but our game was not like it is today.
"That is normal after seven or eight months together — we know each other better. I know the players better, they know me. I feel we are playing quite good."
Guardiola said Sane cannot relax if he wants become one of the best players in the world.
The Germany winger has scored six times in his last 10 games after initially struggling to make an impact following his £37 million move from Schalke.
Guardiola said the 21-year-old is "so fast and runs in behind like few players in the world."
But he added: "But he's just 21 years old, so the gap to become a really good player is still big.
"I can say that because I was the manager of the best player in history [Lionel Messi]. That's why I know he can improve.
"The moment he's going to relax is going to be in another place, not on the pitch, because we want to help him. With this talent it would be a pity not to try to realise all this potential that he has."
Guardiola said City had not had an easy afternoon against a stubborn Sunderland side who hit the post through Jermain Defoe before Sergio Aguero opened the scoring.
"They are the most difficult games," he said. "For these ones they say it will be easy, it will be easy, but it is so complicated.
"We saw that in the first minutes. Sunderland were so aggressive. We were lucky to get to half time 1-0 and after that we controlled the game."